1. Field of the Invention
The present invent[on relates to a light emitting element and a manufacturing method thereof.
2. Description of the Related Art
Semiconductor lasers have heretofore been put into practice as light sources of optical disc, optical fiber communication or the like, and improvements of characteristics such as high coherence, high output and so on are desired. On the other hand, semiconductor lasers are formed as monolithic integrated semiconductors with functional devices such as an optical modulator or the like. In particular, there is a recent demand that semiconductor lasers are formed as two-dimensional integrated semiconductor lasers in a large scale in consideration of a parallel light information processing such as an optical computer or the like and also in consideration of a large capacity parallel light transmission, etc.
Semiconductor lasers of conventional structure cannot be formed as monolithic integrated semiconductor lasers substantially because conventional semiconductor lasers require a cleavage in order to obtain a resonator facet or performance test cannot be made without separation of elements. As semiconductor lasers that can be two-dimensionally integrated in a large scale, a surface emitting type laser which emits a laser beam in the direction perpendicular to the substrate surface receives a remarkable attention.
As a typical arrangement of such surface emitting laser, there is proposed a vertical resonator type surface emitting laser in which a resonator is formed in the direction perpendicular to the substrate surface by laminating a semiconductor layer and a reflection surface on the substrate to thereby emit a laser beam in the vertical direction.
In this case, the resonator is formed in the vertical direction and hence a gain area length is provided in the film thickness direction so that an area that assumes the optical gain is reduced, thereby making it difficult to obtain a high output.
Further, in order to provide a sufficiently low threshold value by forming a distributed reflection type multi-layer above and below an active region as a reflector, it is proposed to render this distributed reflection type multilayer a high reflective index of about higher than 95%. However, in this case, since the amount of light emitted to the outside is decreased, such proposed structure cannot be applied to a high output laser substantially. Furthermore, a p-type distributed reflection type multilayer is relatively high in electrical resistance so that a resistance between the elements cannot be reduced without difficulty.
Furthermore, it is frequently observed that a dielectric multilayer is provided as a reflection film, In this case, a manufacturing process becomes complicated and a current injection cannot be made with ease.
On the other hand, as a structure that can obtain sufficiently high output, there is proposed such one that a 45.degree. reflector is formed near the facet of an ordinary horizontal resonator type laser (e.g., J. Kim et al. Appl.Phys. Lett. 57 (1990), pp. 2048-2050). Although this structure is simple from a theory standpoint, the resonator facet and the 45.degree. external reflector are manufactured by using an etching technique such as RIBE. Therefore, the manufacturing process is complicated and a flatness of the facet and the external reflector and the angle accuracy cannot be controlled without difficulty. There is then the risk that a displacement of an emission angle and an aberration occur.
Furthermore, as another structure that can obtain a sufficiently high output, such an example is reported that, after the ordinary horizontal resonator type laser structure was manufactured, the vertical facet is not formed but an oblique facet is formed as an internal total reflector by the 45.degree. etching process to there! by construct a bend resonator (e.g., N. Hamano et al. Appl. Phys. Lett. 54 (1989), pp. 2389-2391). Even in this structure, the etching technique such as the RIBE or the like is utilized similarly to the above-mentioned external reflector type in the manufacturing process. As a result, a manufacturing process becomes complicated. Also, in this case, there are then the problems of a flatness and angle accuracy of the internal total reflector. Thus, a displacement of an emission angle and an aberration occur.